Physics 0625 · syllabus 4.2
Cambridge IGCSE Physics 0625 — Electrical quantities topical past papers
Electric charge and charging by friction, current as a flow of charge, e.m.f. and potential difference, resistance and R = V/I, and electrical power, energy and the kW h.
- Questions
- 1,322
- Years
- 2009–2026
- With mark scheme
- 99%
- Questions 2022–2026
- 484
Anyone can browse these pages. Opening the questions and their mark schemes takes a free Momentum account.
What Electrical quantities covers
Electric charge comes in two kinds, positive and negative: like charges repel and unlike charges attract. Rubbing a plastic rod with a dry cloth charges both by friction, and only negative charge moves, as electrons pass from one surface to the other, so the object that gains electrons becomes negative and the one that loses them becomes positive. Metals conduct because they contain free electrons that can move; insulators such as plastic and rubber have none. Extended candidates measure charge in coulombs and describe electric fields, regions where a charge feels a force, whose direction is the way a positive charge would be pushed: straight out from a positive point charge or charged sphere, and straight across from the positive plate to the negative one between two parallel plates.
An electric current is a flow of charge; in a metal it is a flow of free electrons. It is measured in amperes with an ammeter connected in series, and it can be direct current, flowing one way only, or alternating current, which keeps reversing. Extended candidates use I = Q/t and know that conventional current is taken to flow from positive to negative, the opposite way to the electrons. The electromotive force (e.m.f.) of a source is the energy it transfers to each coulomb of charge it drives round a complete circuit, and the potential difference (p.d.) across a component is the energy each coulomb transfers to that component as it passes through; both are in volts, measured with a voltmeter connected in parallel, and Extended candidates use E = W/Q and V = W/Q.
Resistance is the p.d. across a component divided by the current through it, R = V/I, found with a voltmeter and an ammeter. A longer wire has more resistance and a thicker one less, and Extended candidates use these proportionalities and sketch current–voltage graphs: a straight line through the origin for a resistor at constant temperature, a curve that flattens as a filament lamp heats up, and almost no current through a diode in the reverse direction. Electrical power is P = IV and energy E = IVt. Energy from the mains is sold in kilowatt-hours, 1 kW h being the energy a 1 kW appliance transfers in one hour.
In the syllabus
The headings this topic has in the Cambridge International 2026–2028 syllabus, as the board prints them.
- 4.2 Electrical quantities
What you should be able to do
- Describe charging by friction as a transfer of electrons, and how to detect a charge
- Explain the difference between conductors and insulators with the free-electron model, and test which is which in a simple circuit
- Use I = Q/t and give the directions of conventional current and of electron flow (Extended)
- Explain e.m.f. and p.d. as energy per unit charge, and use E = W/Q and V = W/Q (Extended)
- Use R = V/I, describe how to measure a resistance, and explain how a wire's length and thickness affect it
- Use P = IV and E = IVt, and calculate the cost of electricity in kilowatt-hours
Key ideas
- Charging by friction moves only electrons: gaining electrons makes an object negative
- Current I = Q/t, in amperes, 1 A = 1 C/s (Extended); resistance R = V/I, in ohms
- E = W/Q and V = W/Q, in volts; 1 V = 1 J/C (Extended)
- A wire's resistance is proportional to its length and inversely proportional to its cross-sectional area (Extended)
- Power P = IV; energy E = IVt; 1 kW h = 3.6 × 10⁶ J
How Electrical quantities has been examined
From 2022 to 2026, Electrical quantities was on Paper 4 · Theory (Extended) in 14 of 14 exam series, worth about 17% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice (Core) | 183 | 14% | 14 of 14 |
| Paper 2 · Multiple Choice (Extended) | 170 | 13% | 14 of 14 |
| Paper 3 · Theory (Core) | 47 | 14% | 14 of 14 |
| Paper 4 · Theory (Extended) | 52 | 17% | 14 of 14 |
| Paper 6 · Alternative to Practical | 32 | 25% | 13 of 14 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1. The bank files this topic together with neighbouring ones, so these figures count every question in its chapters, including some on those topics.
Filed in Momentum under: Electricity.
A worked example
A 2.0 kW kettle runs on a 230 V supply and takes 3.0 minutes to boil. Find the current, the charge that flows and the energy transferred in one boil, and the cost of 120 boils at 25 cents per kW h.
- Current I = P/V = 2000 / 230 = 8.7 A
- Charge Q = It = 8.7 × 180 = 1.6 × 10³ C
- Energy E = IVt = Pt = 2000 × 180 = 3.6 × 10⁵ J for each boil
- In kW h: 2.0 kW × 0.050 h = 0.10 kW h for each boil, so 120 boils use 12 kW h
- Cost = 12 × 25 = 300 cents
Answer: 8.7 A; about 1.6 × 10³ C; 3.6 × 10⁵ J for each boil; 300 cents for 120 boils
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Saying positive charges or protons move when a rod is rubbed — only electrons move, so a rod becomes positive by losing electrons
- Connecting an ammeter in parallel or a voltmeter in series — the ammeter goes in line with the current, the voltmeter across the component
- Mixing units in an electricity bill — energy in kW h needs the power in kW and the time in hours, not watts and seconds
- Finding a filament lamp's resistance from the gradient of its I–V graph — resistance is V ÷ I at the point you read, and it rises as the lamp heats up
- Saying a thicker wire has more resistance — a larger cross-sectional area gives the electrons more room to flow, so the resistance is lower
Exam technique
- When defining e.m.f. and p.d., use 'energy transferred per unit charge' and say whether it happens in the source or in a component
- Give every answer its unit: C, A, s, V, J, Ω, W or kW h
- For an electricity bill, work out kW h = power in kW × time in hours, then multiply by the price of each kW h
- On I–V sketches, label both axes, show both directions of current, and keep the diode's reverse current close to zero
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.